Structural properties ofSr0.61Ba0.39Nb2O6in the temperature range10–500Kinvestigated by high-resolution neutron powder diffraction and specific heat measurements

Abstract

We report high-resolution neutron powder diffraction on ${\mathrm{Sr}}_{0.61}{\mathrm{Ba}}_{0.39}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}$ in the temperature range $15--500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The results indicate that the low-temperature anomalies $(T\ensuremath{\leqslant}100\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ observed in the dielectric dispersion are due to small changes in the incommensurate modulation of the $\mathrm{Nb}{\mathrm{O}}_{6}$ octahedra, as no structural phase transition of the average structure was observed. This interpretation is supported by specific heat measurements, which show no latent heat, but a glass-like behavior at low temperatures. Furthermore, we find that the structural changes connected with the ferroelectric phase transition at ${T}_{c}\ensuremath{\simeq}350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ start already at $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, explaining the anisotropic thermal expansion in the temperature range $200--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ observed in a recent x-ray diffraction study.